Methicillin-resistant Staphylococcus aureus (MRSA) is becoming an increasingly problematic micro-organism, with infection rates rising and effective methods of control becoming more and more limited. In addition to the resistance of MRSA to antibiotics, there is a significant problem due to the availability of few effective sterilisation methods for environmental decontamination; for example in air and on contact surfaces. Public and media interest in the transmission and control of MRSA is escalating and it is becoming one of the most significant problems within the healthcare industry. Hospitals and nursing homes are the worst affected areas. Furthermore, community-acquired MRSA is also now being recognised as an increasing problem, with transmission occurring in public and social areas such as public gyms and sports centres.
As well as MRSA, other Gram-positive bacteria are known to cause health problems, particularly in the hospital environment. For example, Staphylococcus epidermidis, which is a Coagulase-Negative Staphylococcus (CONS), can cause infection, particularly in infants and in hospitalised patients who have received prosthetic implant surgery. Streptococcus pyogenes is a Gram-positive coccus commonly associated with infections such as pharyngitis, pyoderma, scarlet fever, erysipelas, cellulitis, streptococcal toxic-shock syndrome, rheumatic fever, glomerulonephritis, bacteraemia and necrotizing fasciitis, often referred to as “flesh-eating bacteria”. Enterococcus faecalis (another Gram-positive coccus) is a common cause of urinary tract and wound infections, as well as other infections including bacteraemia, endocarditis and meningitis in severely ill hospitalised patients. Multi-antibiotic resistance is also becoming a well-documented problem with enterococcal infections. Clostridium species, in particular C. difficile, have been associated with high mortality in elderly patients due to diarrohea-associated dehydration, medically known as antibiotic-associated pseudomembranous colitis.
Many techniques have been proposed for destroying harmful bacteria, such as MRSA. For example, U.S. Pat. No. 6,251,127 describes a photodynamic process for the inactivation of bacteria and fungal wound infections using methylene blue or toluidene blue. Light energy in combination with photosensitising agents is used to treat or detect pathologies of living tissue, including cancer and microbiological pathogens. The light used has wavelengths ranging from about 450 nm to about 850 nm. Tests demonstrate the efficacy of the light treatment in combination with the photosensitising agents for the destruction of Staphylococcus aureus in in-vivo infected wounds; and for in-vitro destruction of antibiotic-resistant Staphylococcus, Streptococcus, Enterococcus, E. coli, Pseudomonas, Haemophilus influenza and Candida albicans. In addition, wavelength spectra of activation of methylene blue and toluidene blue in the presence of various concentrations of the above bacteria and Candida have been provided.
Whilst in some environments, the methodology of U.S. Pat. No. 6,251,127 may be useful, it nevertheless suffers from the significant practical disadvantage that photosensitising agents must be applied to the bacteria that are to be inactivated. A similar problem arises with US2005/0049228, which also requires the combined use of a photosensitiser and light; in this case, in the range of 500 nm to 580 nm. The need for photosensitising agents is a significant limitation of these techniques.
An objective of the present invention is to provide a simple and effective technique for inactivating selected bacteria, in particular MRSA, and more generally the Staphylococcus, Streptococcus, Enterococcus and Clostridium species.